Percentages: The most useful statistics ever invented

If 10% of smokers get lung cancer and 2% of non-smokers get lung cancer, you can’t just “split the difference” between those two numbers to get the % of people in general who get lung cancer by adding them together and dividing by two (to obtain 6%). The number of non-smokers far exceeds the number of smokers (at least in 2009), so the percentages have to be weighted before averaging ... ................
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